The fourth novel in the classic Legion of Space series.

In swarming hordes they poured forth from the core of the Nebula: the shadowflashers - nightmarish parasites bent on enslaving the minds and bodies of the entire human race. Already they had killed the Keeper of the Peace, and stolen the great secret weapon Akka. Now nothing stood between Mankind and the ultimate destruction...

It was Jil Gyrel who first sensed danger. Daughter of a lost Legion pilot, Jil had inherited her father's uncanny gifts of navigation - and his courage. But what was one girl's bravery against the most monstrous evil ever to emerge from the treacherous oceans of space?